In most golf balls, a plurality of dimples are arranged on their surface. Many attempts have been made to tailor the shape and arrangement of dimples for the purpose of improving the aerodynamics of the flight of golf balls, specifically maximizing the flight distance while preventing the golf ball from turning aside in a vertical or lateral direction. The common approach employs either dimples of one type which are circular as viewed in a plane or dimples of plural types which differ in diameter and/or depth. In some cases, non-circular dimples such as polygonal or elliptic dimples are combined with circular dimples. The dimples are arranged throughout the ball surface as uniformly as possible by utilizing polyhedral arrangement patterns.
Commonly used in the molding of golf balls is a mold of the type that is divided at an equator plane into a pair of mold sections which are mated to define a spherical cavity, the cavity being provided on the inner wall surface with a plurality of protrusions for shaping dimples. For the convenience of working of such molds, no dimple-shaping protrusions are located in the parting plane where the mold is divided. As a consequence, an endless land where no dimples lie is formed along the equator of the golf ball. This endless land interrupts the continuity of dimple arrangement between one hemisphere and the other hemisphere of the golf ball. Then the golf ball lacks the uniformity of flight performance that the ball when hit travels straightforward independent of the spinning direction in flight.
Golf balls which are improved in flight uniformity by laying dimples on the equator have been proposed as described in JP-A 2001-321460. In golf balls of such prior art approaches, to avoid a complication of mold manufacture, the dimples lying on the equator of the ball in alignment with the parting line of the mold must be limited to circular ones, and the number of the dimples lying on the equator must be minimized. An attempt to further improve the golf ball having some dimples laid on the equator, that is, an attempt to improve the uniformity of dimple arrangement and increase the density of dimple arrangement results in an increased expense of mold manufacture due to complication. Given this drawback, for most of the currently available golf balls, the degree of freedom of dimple arrangement is restricted in consideration of the ease of mold manufacture.